1. Field of the Invention
The present invention relates to a blow-by gas recirculation system for an internal combustion engine, and more particularly to a blow-by gas recirculation system which comprises an intake unit provided with a throttle valve and an intake passage and disposed on the side of one of opposite sidewalls of an engine body, an oil separation cover defining an oil separation space in cooperation with the one sidewall, and a positive crankcase ventilation (PCV) valve attached to the oil separation cover, wherein the system is designed to separate oil from blow-by gas introduced from an inside of the engine body into the oil separation space and supply the blow-by gas to a region of the intake passage downstream of the throttle valve.
2. Description of the Related Art
During a course of combustion in an internal combustion engine (hereinafter referred to simply as “engine”), unburned gas leaked from combustion chambers into a crank chamber defined inside a cylinder block and an oil pan, so-called “blow-by gas”, is generated. It is a common practice to collect such blow-by gas and recirculate the blow-by gas to an intake system to re-subject it to a combustion process. The collected blow-by gas contains lubricating oil in the form of a mist. Thus, if it is insufficient to separate the oil component from the collected blow-by gas, the residual oil is likely to cause adverse effects on a catalyst in an exhaust system.
For this reason, a blow-by gas recirculation system has been commonly employed which is adapted to introduce blow-by gas into an intake system after separating oil from the blow-by gas, in such a manner that an oil separator chamber is provided in an engine body to separate oil from blow-by gas, and a positive crankcase ventilation valve (hereinafter referred to as “PCV valve”) is connected to the oil separator chamber and further connected to the intake system via a positive crankcase ventilation hose (hereinafter referred to as “PCV hose”). In this blow-by gas recirculation system, moisture contained in the blow-by gas is likely to freeze due to cooling of the PCV valve and the PCV hose by wind created under driving conditions at extremely low-temperatures, and thereby adversely affect a blow-by gas recirculation capability.
Moreover, as recent trends, an intake manifold and an oil separator chamber-defining member have been increasingly made of a synthetic resin material to facilitate a reduction in cost and weight and a compact layout. In this case, heat conduction from an engine body is reduced as compared with the case where they are made of a metal material, and thereby the freeze phenomenon will become more prominent.
As measures against this problem, for example, there has been known a structure disclosed in JP 2002-106429A (hereinafter referred to as “Patent Document 1”). Specifically, in the structure disclosed in the Patent Document 1, an engine is arranged in a direction transverse to a frontward-rearward (i.e., longitudinal) direction of a vehicle while allowing a resin intake manifold to be oriented toward a front end of the vehicle, and a concave portion formed in one of opposite sidewalls of the engine is covered by a resin cover to define an oil separator chamber therebetween, wherein a PCV valve and a PCV hose are arranged to fall within a projected area of the intake manifold when viewed rearwardly from the front end of the vehicle.
In the structure disclosed in the Patent Document 1, the PCV valve and the PCV hose are arranged to fall within the projected region of the intake manifold located frontward of the PCV valve and the PCV hose in the longitudinal direction of the vehicle. This makes it possible to prevent deterioration in blow-by gas recirculation capability due to wind created under driving conditions, even employing the resin intake manifold and the resin oil separator chamber-defining cover.
Although the above system has such advantage, there is still a need for preparing a PCV hose for recirculating blow-by gas to an intake manifold, and reliably reducing a rate of defective assembling of a PCV hose during a production process to guarantee a desired recirculation capability of the PCV hose.
Recent years, in addition to the trend toward synthetic resin intake manifolds, an electronically controlled throttle body has been increasingly employed in view of improvement in engine operability/controllability. This electronically controlled throttle body is equipped with a motor for driving a throttle valve and other components, and therefore a weight thereof including a housing becomes fairly large. Thus, in order to fixedly support the electronically controlled throttle body to an intake system, it is necessary to improve a connection structure to the intake manifold and additionally provide a member, such as a stay, for improvement in supporting strength of an intake manifold itself relative to an engine body. Therefore, an available space around the engine, particularly the intake system, is extremely restricted to make it harder to ensure a layout and an assembling operation of a PCV hose.
JP 2000-008827A (hereinafter referred to as “Patent Document 2”) discloses a PCV passage structure wherein an upstream end of an intake manifold is arranged adjacent to a cylinder head. In the Patent Document 2, a stiffner (cover member) is additionally attached to a head cover covering an upper portion of the cylinder head, and a PCV valve is installed inside a pipe-shaped portion of the stiffner (an extension portion of the stiffner on an opposite side of its attaching flange to the cylinder head and the head cover). Then, the stiffner is connected to the intake manifold at a distal end of the pipe-shaped portion to introduce blow-by gas in a breather chamber into the intake manifold via the pipe-shaped portion.
However, considering the structure disclosed in the Patent Document 2 in terms of stability in mounting strength of an intake manifold to an engine body, a need for further improvement still remains.